Xerko, is played by Lyle Waggoner, and is a famous Orkan idol of Mork's, who appears in the Season 3 episode of Mork & Mindy titled "There's a New Mork in Town" (episode #13).
About Xerko[]
Xerko is a "young" (remember, Orkans age in reverse), middle-aged, but handsome, strappingly built, and famous Orkan who attempted to take Mork's job as Ork's Observer to Earth.
A genius, who apparently excels at everything he turns his hand to (creating the H28 transport beam, composing the Orkan Planetary Anthem), Xerko has taught himself about Earth, humans, and human emotions beyond that even Mork has managed yet, simply from studying Mork's reports and Earth broadcasts, and has developed an interest in both Earth and Mindy because of it.
Because of his achievements, he is Mork's Orkan idol, and his visit to Earth puts Mork in hero worship mode. It is only when Xerko announces to Mork & Mindy together that he is there to challenge Mork to a Holitacker, to replace him so he can help guide Earth's path forward, and evidently make inroads with Mindy that Mork realizes the full implications to him personally.
Like Mork, Xerko also shows his emotions. But unlike Mork he is supremely confident to the point of arrogance, and convinced his place is at he forefront of everything, so does not take well to Mork (of all people) making a stir on Ork, with his reports about Earth starting to become massively popular.
Xerko is also not, unlike Mork, shy in coming forward with Mindy, making increasing overtures to her, including grabbing and kissing her, and encouraging her to wear tight clothes for him. Not something Mindy, already unhappy with how his presence is affecting Mork, takes kindly to. Nor is she happy with how easily he is able to charm Fred, her father won over by how effortlessly Xerko fits into Earth society, able to design his own (dapper) human clothes, and talk effortlessly about Stravinsky and Schubert, showing a great appreciation for music.
Mork, who idolizes Xerko, winds up, after Mindy encourages and supports him in the belief he has the chance to win, taking him on in the Hollitacker, "dueling" him with the Invisible Swords of Cletus, which he wins after snatching victory from the jaws of defeat.
However, even in defeat Xerko manages to turn it into a a personal victory for himself, garnering one notable human emotion, humility, which he feels will make him even more perfect then he was before. He is however gracious in his defeat to Mork, acknowledging that he fought well, and wishing him and Mindy both well, before he heads off to find some other world to bring his leadership skills to.